Prophylaxis with respiratory syncytial virus F-specific humanized monoclonal antibody delays and moderately suppresses the native antibody response but does not impair immunity to late rechallenge

Respiratory syncytial virus (RSV) is the most significant viral cause of lo wer respiratory tract disease in infants and children, This study tested th e hypothesis that a humanized murine monoclonal antibody (MAb) would protec t against RSV infection in mice and have minimal suppressive effect upon th e immune response because it is directed against a single epitope, A humani zed murine MAb (RSHZ19) was tested for both prophylaxis and treatment of RS V infection in BALB/c mice and compared with a polyclonal product. Mice wer e rechallenged when passively administered antibody was undetectable (day 1 04), RSHZ19 reduced virus titer and protected against illness when used in prophylaxis and effected rapid virus clearance when used as treatment. Poly clonal antibody was also an effective prophylaxis but required 200 times th e dose in total protein. Peak neutralizing antibody responses were delayed and somewhat suppressed in the prophylactically treated groups, but mice we re protected against infection on rechallenge. Secondary antibody response to rechallenge in passively immunized mice was equal to that in untreated m ice.